Preheat the oven to 400F. Line a baking sheet with parchment paper.
Toss brussels sprouts, olive oil, salt and pepper together on the prepared baking sheet. Roast in the oven until just starting to crisp, about 25-35 minutes, tossing halfway through.
Place chicken breasts, 1 cup salsa verde, chicken stock, juice of two limes, minced garlic, and cumin in the bowl of your instant pot. Cook on high pressure for 20 minutes, the release and shredded chicken. If you don’t have an instant pot, you can combine these same ingredients in a 9x13 baking dish and roast in the oven with the brussels sprouts until the chicken reaches an internal temperature 165F.
Meanwhile, whisk together sour cream and remaining 3 tbsps of salsa verde.
Serve warmed tortillas with shredded salsa verde chicken, roasted brussels sprouts, and queso fresco then top with diced avocado, sliced onions, freshly minced cilantro, and lime wedges, if desired.