Combine the eschalots, garlic, oregano, sugar, olive oil, vinegar, lime juice, tequila, salt and pepper in a resealable bag; shake to combine. Add the tilapia to the mixture and store in the refrigerator 2 to 4 hours, turning every 30 minutes.
Preheat oven to 230 degrees C. Line a baking tray with aluminium foil and prepare the surface with cooking spray.
Arrange the fish on the prepared baking tray. Discard remaining marinade.
Bake in the preheated oven until the fish flakes easily with a fork, about 10 minutes.