Preheat Oven:
Preheat oven to 350°F (175°C). Lightly spray a 9x13x2-inch baking dish with cooking spray.

Cook Ground Beef:
In a large skillet over medium-high heat, cook the ground beef until browned and no pink remains. Break it up as it cooks. Stir in salt and pepper.

Add Vegetables:
Add the diced onion, red bell pepper, and green bell pepper to the skillet. Cook for 3–4 minutes, until onions are translucent. Drain excess fat and remove from heat.

Prep Potatoes:
Peel and thinly slice the potatoes. Place slices in a bowl of cold water to prevent browning. Drain and pat dry with clean paper towels.

Make the Sauce:
In a medium bowl, whisk together the evaporated milk, cream of mushroom soup, and cream of chicken soup.

Layer the Casserole:
In the prepared baking dish, layer half of the potatoes, half the beef mixture, half the sauce, and 1½ cups of the shredded cheese. Repeat the layers using the remaining ingredients, finishing with the remaining 1½ cups of cheese.

Add Fried Onions:
Sprinkle fried onions on top. Cover tightly with foil.

Bake:
Bake covered for 75–80 minutes, or until the potatoes are fork-tender and the internal temperature reaches 165°F.

Broil (Optional):
Remove foil and broil for 1–2 minutes until the top is golden and bubbling.

Rest and Serve:
Let the casserole sit for 10 minutes before serving to help the layers set.