8 oz boneless, skinless halibut, patted dry and cut into 1-oz strips
Olive oil cooking spray
1/3 cup plain Greek yogurt (TRY: Voskos Original Plain Greek Yogurt)
1/3 cup crumbled feta or cotija cheese
Prepare salsa: Arrange oven racks in center and top half of oven, and preheat oven to broil. Place corn on a baking sheet and transfer to top oven rack. Broil, turning once, until kernels are brown and blistered, about 18 minutes. When cool enough to handle, carefully slice kernels from cob. Transfer kernels to a medium bowl. Cut peel and white skin from grapefruit. Working over bowl of corn, use a paring knife to segment grapefruit, adding segments to bowl and allowing juice to drip over kernels. Add cucumber, onion, tomatoes, serrano pepper, zest and juice of 1 lime, oil, cilantro, ¼ tsp cumin and ¼ tsp salt to bowl. Mix well, cover and refrigerate until needed.
Preheat oven to 425°F. Stack tortillas on top of each other and wrap in foil. Place packet on 1 side of a parchment-lined baking sheet.
To a shallow bowl, add flour. In a separate shallow bowl, whisk egg whites, remaining 1/4 tsp cumin and 1/4 tsp salt. In a food processor, pulse rice crisp cereal into a fine powder; transfer to a third shallow bowl. Working 1 at a time, coat each halibut strip in flour, then egg mixture and, finally, cereal. Arrange strips in a single layer on empty side of baking sheet. Mist strips with cooking spray and bake in center of oven for 6 minutes, until coating is golden and fish is cooked through.
Meanwhile, in a small bowl, combine yogurt, feta and remaining zest and juice of 1 lime. Set aside.
To assemble, carefully open foil packet of tortillas. Spoon salsa into center of each tortilla, dividing evenly. Top with halibut and yogurt-feta sauce.