In a medium bowl, mix oil, garlic, Old Bay seasoning, thyme, and lemon zest. Toss with fish, then set aside.
In a slightly oiled Dutch oven, place onion slices on the bottom. Scatter sliced fennel over top.
Pour in 1/2 lemon juice and sprinkle with salt and pepper. Then top with tomatoes and pour in white wine.
Place in oven for 35 minutes, giving a good mix halfway through.
Take out of the oven after vegetables are cooked through, then place the tilapia overtop, nestling among the tomatoes.
Drizzle any leftover marinade over the fish and tomatoes, then place back in the oven and cook for 8-10 minutes, or until fish cooks to desired done-ness.
Remove from oven and drizzle remaining 1/2 lemon juice over fish.
Sprinkle with fennel fronds, then serve over pasta, polenta, or rice, and enjoy!
