Melt the butter in saucepan, whisk in the flour and cook for 1 minute. Whisk in the milk and stir until there are no lumps. Season with salt and white pepper. Continue cooking at low/medium heat until sauce thickens. Add jack cheese, cream cheese and 1/4 cup cotija (or parmesan) cheese, stir to melt, taste for salt. Cover and remove from heat. Preheat oven to 375ºF.
In a large skillet, heat 2 tablespoons olive oil to medium heat. Add the garlic, serrano, poblano, and red bell pepper. Season lightly with salt and pepper and cook for 4-6 minutes. Lower the heat. Add the shrimp, crab, lime juice, 1/2 cup reserved cheese sauce, and sour cream. Stir well to combine, taste for salt and pepper. Remove from heat and fold in the cilantro and green onions.
Lightly spray an 8×8 casserole dish with oil. Start with a layer of cheese sauce (about 1 cup), add 4 corn tortillas to cover the bottom. Add just enough cheese sauce to cover tortillas. Add all the sliced zucchini and season with lemon pepper seasoning. Add half of the seafood mixture from pan.
Repeat the layering (minus the zucchini) until you end up with sauce as the top layer. Top with remaining jack cheese. Bake uncovered for 35 to 40 minutes, then broil for just a minute to brown the cheese slightly. Let the casserole cool for a good 20 to 25 minutes before you cut into it. Garnish with guacamole, salsa, thin sliced red or green onions, radishes and cilantro.
For Rolled Enchiladas:
Brush tortillas with olive oil. Cook on preheated griddle pan for 20 seconds per side. Fill and roll. Add just enough cheese sauce to cover the bottom of a baking dish. Add the rolled enchiladas. Top with cheese sauce and cheese. Bake in preheated 350 degree oven for 25 to 30 minutes or just until cheese melts. Broil for a minute.
Notes
If preparing rolled enchiladas, you can saute the sliced zucchini and serve it on the side.