Preheat your oven to 350°F and lightly coat a 9 x 13 x 2-inch baking dish with nonstick spray.

In a large skillet over medium-high heat, cook the ground beef until it’s fully browned and no longer pink, breaking it into crumbles as it cooks. Season with salt and pepper.

Add the diced onion and both red and green bell peppers to the skillet. Cook for a few minutes, stirring occasionally, until the onion becomes soft and translucent. Drain off any excess fat and remove the skillet from heat.

While the meat is cooking, peel the russet potatoes and slice them thinly. Place the slices in a large bowl of cold water to prevent browning and remove excess starch.

In a separate medium-sized bowl, whisk together the evaporated milk, cream of mushroom soup, and cream of chicken soup until well combined.

Drain the potato slices and gently pat them dry using clean paper towels. Arrange half of the sliced potatoes in an even layer across the bottom of the prepared baking dish.

Spread half of the meat and vegetable mixture over the potatoes, followed by half of the soup mixture. Sprinkle 1½ cups of shredded cheddar cheese evenly on top.

Repeat the layering process with the remaining potatoes, beef mixture, soup mixture, and top it off with the remaining 1½ cups of cheese.

Sprinkle the fried onions evenly over the top layer of cheese. Cover the baking dish tightly with aluminum foil.

Bake for 75 to 80 minutes, or until the potatoes are fork-tender and the casserole reaches an internal temperature of 165°F. Remove the foil and broil on high for 1 to 2 minutes, just until the top becomes golden and crisp.

Allow the casserole to rest for about 10 minutes before serving so the potatoes can absorb the remaining liquid and everything sets nicely.