Beef Stuffed Rainbow Peppers

Ingredients

• 4 large bell peppers (green, yellow, red, and/or orange)
• 1 Tbsp olive oil
• 1/2 C minced onion
• 16 oz lean ground sirloin
• 1/8 tsp celery salt
• 1 tsp fresh ground pepper
• 1 C instant brown rice
• 1 envelope beefy onion soup mix
• 3/4 tsp dried mustard
• 1 (15 oz) can tomato sauce
• 1/2 C shredded cheddar cheese (optional)