Skillet Burgers with Tomato Sauce

Ingredients (12)

• + 1 ½ pounds ground beef add to pantry
• + 2 (8 ounce) cans tomato sauce, divided add to pantry
• ✓ 1 large egg
• + 1 teaspoon salt add to pantry
• ✓ ¼ teaspoon ground black pepper
• + 6 thin slices onion add to pantry
• + 1 tablespoon olive oil, or as needed add to pantry
• + 6 thin slices lemon add to pantry
• + 1 tablespoon Worcestershire sauce add to pantry
• ✓ 1 tablespoon white sugar
• + 1 teaspoon chili powder add to pantry
• + ½ teaspoon mustard add to pantry