In Italy, particularly in Tuscany, pork grilled with herbs (called porchetta) is quite common and every butcher or cook has his/her own personal herb blend that they use to coat or stuff the pork with before cooking. --- The herbs are rubbed onto/into the pork and then typically cooked over a wood-fired grill or hot coals. Sage and rosemary are common herbs for porchetta. 

I like to play around with different herbs and spices, depending on what's fresh and available, and so the "recipe" that follows is more of a series of suggestions than something you need to follow to the letter. Feel free to adjust and customize the recipe to suit your own needs and tastes. For example, most grilled porchetta calls for the use of minced garlic, but I find the garlic too often burns on the grill, so I leave it out. 

There are a couple of do-ahead-of-time steps: brining the pork and making the herb blend. 

Ingredients:

1 3-4 lb. boneless pork loin

Fresh herbs: sage, rosemary, thyme, basil or your favorites

Dried spices: lavender leaves, cracked black pepper, fennel seeds

Kosher salt (both for the pork and for the brine)

Sugar 

Olive oil

Technique: 

First, create a brine for the pork. In a bowl or Zip-loc freezer bag, dissolve 1/4 cup kosher salt and 2 tbsp. sugar into 1 quart of water. This is a basic grilling/high-heat brine. You can increase the amount of brine depending on the size of your pork roast. Simply immerse the pork into the brine and allow the meat to brine in the fridge for about an hour per pound, but not more than 8 hours or the meat can get mushy.

I place the brine bag in a bowl before refrigerating, just in case any leaks out.

Next, make your herb blend.

You can adjust this recipe, depending on how much herb mixture you need. The following is just a rough estimate of amounts -- no need for exact measuring here.

In a small food processor (or you can chop this up by hand), place about a half-cup of sage leaves to 1/4 cup rosemary, along with fresh basil leaves to taste (if available) and fresh thyme leaves (about a tablespoon). Add 1 tbsp. kosher salt and 1/2 tbsp. each lavender leaves and fennel seeds. Again, feel free to toy with these amounts, as you please. You could also add a few peeled garlic cloves at this point, and coriander seeds, juniper berries, mustard seeds, etc.

Pulse the processor until the herb blend is finely minced but still has a bit of rustic chunkiness to it. 

Transfer the mix to a bowl for later use.

Remove the pork loin from the brine and rinse briefly in cold water to remove excess salt. Pat dry and let the loin sit at room temperature for a half-hour to allow it to warm up before cooking. 

Then, on a large plate or platter, sprinkle the pork with a little olive oil then rub the herb blend all over the pork. It'll get a little messy. Keep some paper or cloth towels handy.

When you're ready to cook, bring a grill to high heat. When the grill is hot, sear the pork on all sides to brown it a little.

Then, continue to cook the loin over indirect heat at about 300 degrees F. until the internal loin temperature reaches 140 degrees F. This will take approximately 20-25 minutes per pound, depending on your grill and the size of your roast. 

Remove the pork to a platter or cutting board and cover loosely with aluminum foil, allowing it to rest for 10 minutes. The temperature of the pork will increase some, as it continues to cook in the foil. 

Remove the butcher's twine if the loin has been tied up, slice, and serve with your favorite sides.