If you're making the Avocado Salsa Verde from scratch, start by pulling off the husks of the tomatillos and giving them a good rinse. I usually de-stem them as well. Roast the tomatillos in a 400F oven for 10-20 minutes or until they start to turn army green in color.
Add the roasted tomatillos to a blender along with 1/2 onion, 1 peeled garlic clove, 10-12 sprigs cilantro (using the upper stems is fine), and 1/2 of the jalapeno pepper. (Be sure to give the cilantro and jalapeno a good rinse.) Pulse blend and taste for heat level. If you want more spice add more of the jalapeno. Add the flesh of a single avocado to the blender and combine well. Salt to taste (I typically do not add much salt).
Chop a single chicken breast into bite-sized pieces and combine with the seasoning ingredients in a bowl. The exact seasoning isn't crucial for this dish, but I used 1/2 teaspoon ground chili powder, a pinch of chipotle powder, 1/2 teaspoon Mexican oregano, 1/4 teaspoon salt, freshly cracked black pepper, and a dollop of olive oil. Saute 2-3 Tablespoons of chopped onion in a drizzle of oil over medium-high heat for a few minutes. Add the chicken and form a single layer, leaving it until nearly cooked through. Flip and finish cooking the other side. Set aside until needed.
I usually warm up the tortillas in a large dry skillet for 30 seconds or so before adding ingredients to them. Each tortilla gets rice, cheese, chicken, and plenty of the Avocado Salsa Verde. Roll tight and cook each side of the burrito in the dry skillet for 3-4 minutes per side or until it is crisping up and turning golden brown. (I usually put my stove at medium heat.)
Serve immediately. Store leftover burritos in the fridge, uncooked, wrapped in parchment paper and foil. To reheat, put the wrapped burrito in a 400F oven for 20-30 minutes.