Step 1

Preheat oven to 350 degrees F. Heat oil in a large skillet over medium-high heat. Add onion, poblanos and garlic; cook, stirring occasionally, until softened, 4 to 5 minutes. Add squash, zucchini, corn, pico de gallo and salt; cook, stirring occasionally, until the liquid comes to a simmer, 5 to 6 minutes. Simmer, stirring occasionally, until the liquid reduces by half, about 2 minutes. Remove from heat; stir in pinto beans and black beans.

Step 2

Coat a 9-by-13-inch baking dish with cooking spray. Spoon one-third of the vegetable mixture into the prepared dish. Top evenly with 4 tortillas. Repeat with half the remaining vegetable mixture and the remaining 4 tortillas. Top with the remaining vegetable mixture. Sprinkle evenly with cheese.

Step 3

Bake until the cheese is bubbly, 25 to 30 minutes. Sprinkle evenly with avocado and scallions. Dollop with sour cream.