Pre-heat the oven to 400º F.
In a large, oven-safe pan, heat 1 tablespoon olive oil over medium heat. Add the garlic slices and sauté until slightly soft and fragrant, but not browned, about 30 seconds.
Add the halved tomatoes, ½ teaspoon kosher salt, ½ teaspoon cumin, and ¼ teaspoon pepper and cook over medium-heat, stirring occasionally, for 10 to 12 minutes, until the tomatoes have released their juices and almost completely collapsed.
Remove the tomatoes from the pan completely and place in a small bowl. Add half of the cilantro and the juice of 1 lime to the tomatoes in the bowl and stir to combine.
Wipe out the pan with a paper towel.
Pat the mahi filet completely dry, then season with salt and ¼ teaspoon cumin.
Add 2 tablespoon olive oil to the pan and heat over medium-high heat. Once hot, add the mahi and cook for about 3 minutes on each side until browned, without moving the fish around.
Once both sides are browned, turn off the heat. Add the tomato-cilantro mixture back into the pan, surrounding the browned fish.
Place the pan in the oven at 400ºF for about 5 minutes, until golden on top and cooked through, making sure not to overcook.
Garnish with remaining chopped cilantro.