Preheat the oven to 350°F and position a rack in the middle of the oven. Lightly grease a 9×13-inch deep casserole dish and set aside.

In a large skillet over medium-high heat, add the 1 1/2 pounds ground beef. Let it cook unmoved 1 minute to sear, then break it up with a spoon and cook, stirring, about 5 minutes or until no longer pink.

Drain most of the grease from the skillet, leaving about 2 tablespoons of fat in the pan.

Add the finely diced onion, finely diced green bell pepper, minced garlic, the can (7 ounces) diced green chiles, 3 cups salsa, and 2 tablespoons taco seasoning to the beef. Season with salt and pepper to taste. Stir to combine.

Bring the mixture to a simmer, simmer 2 minutes, then reduce the heat to low and cook 5–7 minutes, stirring occasionally.

In a small bowl, dissolve 2 tablespoons cornstarch in 4 tablespoons water. Pour the slurry into the beef mixture, stir, and cook 2–3 minutes until the mixture thickens, stirring to prevent sticking. Remove the skillet from the heat.

Assemble the lasagna in the prepared dish. For the first layer of tortillas, place two whole 8-inch tortillas in the pan. Cut a third tortilla into four quarters and place one quarter in each corner to fill gaps. Cut a fourth tortilla in half and place each half along the two remaining sides to fully cover the bottom (this uses 4 tortillas).

Spread half of the refried beans (one 16-ounce can) evenly over the tortillas.

Spoon half of the beef mixture evenly over the refried beans.

Scatter half of the rinsed and drained can (15 ounces) black or pinto beans over the beef.

Sprinkle 1 1/2 cups shredded Mexican cheese blend over this layer.

Repeat the tortilla arrangement for the second layer (use 4 more tortillas the same way as step 7).

Spread the remaining refried beans (the second 16-ounce can) evenly over the second layer of tortillas.

Spread the remaining beef mixture evenly over the refried beans.

Scatter the remaining rinsed and drained black or pinto beans over the beef.

Sprinkle the remaining 1 1/2 cups shredded Mexican cheese blend over this second layer.

Place the final layer of tortillas (the last 4 tortillas) on top to cover the casserole.

Spread 1 cup salsa evenly over the top layer of tortillas, then sprinkle 1 cup shredded Mexican cheese blend over the salsa.

Bake in the preheated oven for 30 minutes. After 30 minutes, switch the oven to broil and broil 2–3 minutes, watching closely, until the top cheese is golden brown and bubbly.

Remove the lasagna from the oven and let it cool on a rack 30–40 minutes before slicing and serving.