Place lemon in a small bowl and microwave for a few minutes to release the essential oils. The lemon will be hot coming from the microwave, so set aside until it is just cool enough to handle. Heat the olive oil over medium-high heat in a medium saute pan, and saute the red, yellow and green bell peppers. Add the red onion and the chili flakes and saute until they begin to soften. In a blender, puree stewed tomatoes, balsamic vinegar, and hot sauce. Leaving the blender running squeeze the lemon juice from the micro-waved lemon (after removing seeds) through the feed opening. Transfer this mixture to the pan of peppers and onion and cook over medium heat, allowing to reduce by half. Remove from heat and let cool to room temperature.
Heat the oil in the deep-fryer to 375 degrees F, or as directed in the manufacturer's instructions for similar foods. Combine flour, salt, black pepper, and garlic powder and dredge the snapper and grouper fillets in this mixture, shaking off any excess. Deep-fry the fish until golden brown, and remove to paper towels to drain.
Arrange the fish along each side of a long platter and spoon the escabeche down the middle. Garnish with scallions.