Prepare the ranchero sauce and refried beans in advance if using homemade, or have prepared versions ready.
Heat 1 tablespoon olive oil in a large skillet over medium heat. Add the chopped onion and cook until soft, about 4 minutes. Stir in the minced garlic and cook 30 seconds more.
Add the ground beef and cook, breaking it up, until no longer pink, about 8 to 10 minutes. Spoon off and discard all but about 1 tablespoon of rendered fat.
Add the chili powder, cumin, oregano, garlic powder, onion powder, smoked paprika, cayenne, Kosher salt, and black pepper. Cook, stirring, until aromatic, about 1 to 2 minutes. Stir in 1 tablespoon flour and cook 1 minute.
Stir in the 15 oz can Ro-tel tomatoes (with juice) and 1 cup beef broth. Bring to a simmer and cook until slightly thickened and most liquid has reduced, about 10 minutes. Remove from heat and set aside.
Heat about 1 inch of vegetable oil in a large saucepan or deep skillet to 350°F (175°C). Meanwhile preheat the oven to 425°F (220°C).
Warm the 2 cups refried beans in a saucepan until heated through. Briefly warm the tortillas so they are soft and pliable.
Assemble each chimichanga: on one half of a tortilla spread 1/4 to 1/2 cup refried beans leaving a 1-inch border. Top with roughly the same amount of beef filling and a sprinkle of shredded cheddar.
Fold the sides of the tortilla in about 1 inch, then roll tightly from the filled side, tucking the ends in. Secure with 1 or 2 toothpicks if needed.
Working in batches, carefully lower 1–2 chimichangas into the 350°F oil using metal tongs. Fry until golden on one side, flip and fry until golden all over, a couple of minutes per side. Remove to paper towels to drain.
Place fried chimichangas on a baking sheet. Spoon about 1/2 cup ranchero sauce over each, sprinkle with a little extra cheddar, and bake 3 to 5 minutes until cheese is melted and bubbly.
Remove from oven, discard any toothpicks, and serve immediately with sour cream, pico de gallo, and salsa as desired.