Finely mince garlic, onion, and peppers, taking care not to touch peppers with the fingers. (Use a fork to hold them while chopping.)
Put garlic, onion, and peppers into a jar. Add 1/2 teaspoon salt and enough oil to cover them. Let mixture sit overnight or longer. (It will keep for a month or more in the refrigerator).
Fry banana slices in hot oil. Drain excess oil and salt to taste.