Preheat your oven to 400°F and line a baking sheet with parchment paper for easy cleanup.
Slice the carrots into thin rounds and place them on the baking sheet along with the whole cherry tomatoes.
Drizzle the vegetables with half of the olive oil and a pinch of salt and pepper, then roast for 15 minutes until the tomatoes are blistered.
Pat the tuna steak and cod fillet dry with paper towels and season both sides with sea salt, black pepper, and dried oregano.
Heat the remaining olive oil in a cast-iron or non-stick skillet over medium-high heat until shimmering.
Place the cod in the pan and sear for 3 minutes per side until golden and flaky, then remove from the heat.
Sear the tuna steak for 90 seconds to 2 minutes per side to achieve a perfect medium-rare center.
Flake the whitefish and slice the tuna into thin strips, then toss them gently with the fresh lemon juice.
Warm the whole wheat pita in the oven for 1 minute, slice it open, and stuff it generously with the fish and roasted vegetable mixture.