Combine all the ingredients in a mixing bowl - watermelon, tomato, avocado, onion, garlic, jalapeno, basil, lemon juice, salt, and pepper - and mix well. Place in the fridge until ready to serve.
Using a paper towel, pat the fish completely dry and set aside.
In a small bowl, mix the salt, oregano, basil, thyme, garlic powder, pepper, and lemon zest.
Heat the olive oil in a medium pan over medium heat. Just before you add the fish, season only one side of each fillet with some of the seasoning mix.
Place the fillet in the pan, seasoned side down. Allow the fish to cook until the fillets turn white on the sides, about 4-5 minutes. The fish should lift from the pan easily.
Just before turning the fillets over, coat the side facing up with the seasoning mix. Allow the fish to cook for another 3-4 minutes.
When the fish is complete, remove the fillets to. Add some baby spinach and top with the Watermelon Avocado Salsa and drizzle some balsamic glaze over the fish, salsa, and spinach.