Heat oil and butter in a large pan over medium-high heat. Add tomatoes, onion, and garlic. Saute until tomatoes release all their juices, about 3 minutes. Add tuna, salt, and cumin. Saute for 1 minute. Stir in eggs and cilantro; cook until eggs are set, 3 to 5 minutes.
Spoon 3 tablespoons of the tuna mixture onto each corn tortilla. Top each with a slice of avocado, lime juice, and hot sauce.