Pre-heat a 10 inch Dutch oven to 400 degrees F (25 coals total = 17 on top of lid/8 below bottom of oven).
Heat butter and oil in bottom of pot.
Sauté onions and garlic.
Add the dried spices.
Beat the egg mixture in separate bowl, then pour it over the garlic and onion mixture in the Dutch oven.
Rotate while baking with lid on for about 7-10 minutes until the frittata is almost firm.
Add the cheese to top of frittata, replace lid and continue cooking until cheese is melted and frittata is firm.
Remove from heat and top with avocado, tomatoes and basil just before serving warm.
Notes
*NOTE: You can use a larger oven, just remember the smaller the oven the thicker the frittata and vice versa. You'll need to adjust the number of coals to maintain 400 F degrees for the size of oven you are using. Check our chart https://www.campingforfoodies.com/dutch-oven-temperature-chart/