1 tablespoon olive oil
1 1/2 pounds ground round
1 cup chopped sweet onion (about 1 small onion)
1 tablespoon tomato paste
2 tablespoons all-purpose flour
1 cup beef broth
1 (10-oz.) can diced tomatoes and green chiles, drained
1 tablespoon spicy brown mustard
2 teaspoons Worcestershire sauce
1 1/2 teaspoons kosher salt
1/4 teaspoon black pepper
4 ounces Monterey Jack cheese, shredded (about 1 cup), divided
4 ounces mild Cheddar cheese, shredded (about 1 cup), divided
Cooking spray
4 cups frozen tater tots (from 1 [32-oz.] pkg.)
4 cooked thick-cut bacon slices, crumbled (about 1/2 cup)
Chopped fresh chives
Ketchup (optional)
Preheat oven to 400°F. Heat oil in a large skillet over medium-high; add ground round and onion, and cook, stirring often, until beef is crumbled and no longer pink and onion is tender, 7 to 8 minutes. Drain all fat from skillet, and place over medium.
Add tomato paste to beef mixture in skillet, and cook, stirring often, 1 minute. Sprinkle beef mixture with flour, and cook, stirring constantly, 1 minute. Gradually add broth, and cook, stirring constantly, until mixture thickens, 3 to 4 minutes. Stir in diced tomatoes and chiles, mustard, Worcestershire sauce, salt, and pepper, and cook, stirring often, until mixture begins to simmer, about 2 minutes. Stir in 1/2 cup each of Monterey Jack cheese and Cheddar cheese, and cook, stirring often, until cheeses melt, 1 to 2 minutes. Spoon mixture into a lightly greased (with cooking spray) 11- x 7-inch baking dish. Top evenly with tater tots. Place dish on a rimmed baking sheet.
Bake in preheated oven, uncovered, until bubbly around edges and potatoes are golden brown, 30 to 35 minutes. Sprinkle top with remaining 1/2 cup each of Monterey Jack cheese and Cheddar cheese, and bake until cheese is melted, about 3 more minutes. Remove from oven, and let stand 10 minutes. Sprinkle casserole with crumbled bacon, and garnish with chopped chives. Drizzle with ketchup, if desired.