In a heavy, large Le Cruset pot or dutch oven, sauté the bacon until browned. Add oil, stir, then add the onion and celery until onion is transparent. Add the bay leaves, thyme, garlic, lemon-pepper, and Tony Chachere's seasoning, stir well, and saute for 1 minute.
Add the chicken or fish stock, okra/tomatoes, and canned tomatoes. Cover the pot and simmer gently for 30 minutes. Remove the pot from heat and stir in the shrimp.
Preheat oven to 400 degrees F.
While gumbo is simmering, prepare the topping. In a bowl, mix together the beaten eggs and milk, then add the muffin mix and stir until just blended. (Note: I prefer cornbread which is not sweet, so I use my own cornbread recipe.).
Drop the cornbread dough by tablespoons-full on top of the hot gumbo mixture in the pot, leaving the center un-covered. Place in preheated oven for 20 to 25 minutes and bake, uncovered, or until a knife comes out of the cornbread clean.
If you like, you can prepare this dish the traditional Southern way by using a deep iron skillet to bake it in, but you can also bake it In a pan with an ovenproof handle. You can also use frozen okra in place of the canned - the resulting casserole will be less soupy and nicely thick. Chicken may be substituted for the shrimp, as well; if using, add the cubed chicken before to 30 minute simmer.
Note: depending on the size of the pot you use to bake the casserole in, you might end up with some leftover cornbread dough. Just bake up some more cornbread muffins with the leftover! :).