Keto tuna casserole

 Ingredients

• 1 oz. butter
• 1 (4 oz.) yellow onion, finely chopped
• 1 (5 oz.) green bell pepper, finely chopped
• 5½ oz. (1½ cups) celery stalks, finely chopped
• 1 lb tuna in water, drained
• ¾ cup mayonnaise
• 1 cup (2¾ oz.) shredded Parmesan cheese
• 1 tsp chili flakes
• salt and pepper

Instructions

1. Preheat the oven to 400°F (200°C). Fry onion, bell pepper and celery in butter in a large frying pan until slightly soft. Season with salt and pepper.
2. Mix tuna, mayonnaise, parmesan cheese, and chili flakes in a greased baking dish. Add fried vegetables and stir.
3. Bake for 15-20 minutes or until golden brown.
4. Serve with baby spinach.