Mash boiled plantains. Add 1/4 cup of the olive oil and the butter. Season with salt and freshly ground black pepper. Set aside.
Heat large saute pan with the remainder of the olive oil on medium-high heat. Once the oil is warm add onions, garlic, peppers, celery, and jalapeño to pan and cook for 5 minutes.
Layer a gratin pan with 1/2 of the mashed plantains and 2/3 cup of the cheese. Then add the sauteed vegetables and another 2/3 cup of the cheese. Layer with the rest of the plantains and top with the rest of the cheese.
Bake in a 350 degree Fahrenheit oven for about 10 minutes, or until golden brown. Serve warm garnished with avocado.