Preheat oven to 350° Fahrenheit. Lightly grease 9x13 baking dish with olive oil.
While oven is heating brown lean ground beef in a large skillet over medium heat. Add diced onion, bell pepper, salt, pepper and garlic while browning. Drain away any excess fat using a colander. Set aside.
In a medium sauce pan, warm the 1/2 & 1/2 on low heat. Stir in the Ranch dressing. While constantly stirring, slowly add the grated cheddar cheese. Stir until cheese is completely melted and completely incorporated into the cream. Set aside.
Using either a mandolin or a sharp knife, slice the potatoes into 1/2" thick medallions.
Line the bottom of the baking dish with potato medallions, allowing them to overlap slightly. Sprinkle with extra salt. Cover with 1/2 of the beef. Pour 1/2 of the cheese sauce on top. Using the back of a spoon, massage the sauce a little to work it down into the beef. Repeat to create a second layer of beef and potatoes.
Top with a layer of overlapping potatoes, salt and the Colby Jack cheese. Bake in preheated oven for 50 minutes to an hour until the edges are golden and bubbly.