2 medium tomatoes, chopped (approximately 3/4 cup)
2 ripe avocadoes, pitted, peeled and cubed
8 corn tostadas
1/2 cup crumbled feta cheese
01For the salsa, in a large bowl, gently toss the watermelon, red onion, lime juice and cilantro. Cover with plastic wrap and refrigerate until serving, up to 1 hour.
02 For the fish, sprinkle 1 tablespoon of the blackening spice evenly on both sides of each fillet. In a large, nonstick skillet over medium-high heat, heat the oil. Add 2 fillets and cook approximately 3 minutes on each side until cooked through. Transfer to a plate and keep warm. Repeat with the remaining 2 fillets.
03For the tostadas, divide the cabbage, tomatoes, and avocados among the 8 tostadas. Top each tostada with half a fish fillet and about 1/4 cup watermelon salsa. Sprinkle each tostada with 1 tablespoon of feta cheese. Serve immediately.