Start by making the tender chicken filling. Cook a few boneless, skinless chicken breasts however you prefer (baked, grilled, poached) until cooked through. Once cooled, shred or dice the chicken.
Prepare your ingredients. Dice the jalapeños, onions, and garlic, then shred the cheese.
Use a large cast iron skillet or Dutch oven, to sauté the diced onion, jalapeños, and minced garlic cloves over medium heat until soft and fragrant.
Add them to a large mixing bowl along with the shredded chicken, tomatillo salsa, and chopped cilantro. Season with spices like salt, black pepper, garlic powder, cayenne pepper, and chili powder to taste.
Let the chicken mixture cool slightly and then set up your workstation.
Warm the flour tortillas briefly to make them pliable. Place a big scoop of the chicken filling in the center of each tortilla. Top it with shredded Monterey Jack cheese.
Fold the bottom of the tortilla up and over the filling, then fold in both sides and roll up tightly into a burrito shape.
Add an inch of vegetable oil to a large skillet or Dutch oven. Bring it to medium-high heat. Once the oil is hot, carefully place the chimichangas in the oil seam side down.
Turn frequently until crispy and golden brown on all sides, about 2-3 minutes per side. Keep an eye on the oil temperature. If the chimichangas start to brown too quickly, you may need to lower the heat.
Transfer the fried chimichangas to a paper towel-lined plate or baking sheet to drain excess grease. You can keep them warm in a 200°F oven while you fry the remaining burritos.
Serve the hot chimichangas drizzled with Creamy Jalapeño Ranch Sauce and topped with fresh guacamole, a dollop of sour cream, and Homemade Pico de Gallo.