Combine the diced tomatoes, chopped red onion, chopped cilantro, lime juice, olive oil, salt, black pepper, and minced jalapeño (if using) in a bowl. Stir to mix, cover, and let sit at room temperature for at least 15 minutes or refrigerate up to 2 hours. Stir again before serving.

Roasted Tomatillo Sauce

Roast

Preheat broiler (or a hot oven) to high. Toss tomatillos, jalapeño, garlic cloves, and onion with 1 tsp neutral oil on a rimmed baking sheet. Broil or roast until blistered and lightly charred, 6–10 minutes, turning once to char evenly.

Blend

Transfer the hot roasted tomatillos, chile, garlic, and onion to a blender or food processor. Add cilantro, lime juice, 3/4 tsp salt, and 2 tablespoons water. Blend until smooth, adding more water 1 tsp at a time if needed to reach a pourable sauce consistency. Taste and adjust salt or lime as desired. Let cool to warm before using.

Fish

Season

Pat fish strips dry with paper towels. In a bowl, toss fish with 1 tablespoon olive oil, cumin, smoked paprika, garlic powder, 3/4 tsp salt, and 1/4 tsp black pepper until evenly coated. Let sit 5 minutes to absorb seasoning.

Cook

Heat a large nonstick or cast-iron skillet over medium-high heat until hot. Add a thin film of oil if skillet is dry. Add fish strips in a single layer, cooking 2–3 minutes per side until opaque and flaky and lightly browned. Work in batches if needed to avoid crowding. Remove cooked fish to a plate and squeeze a bit of lime over the top.

Fries (side)

Prepare

Preheat oven to 425°F (220°C) if roasting. Toss cut potatoes with 2 tablespoons vegetable oil, 3/4 tsp salt, and smoked paprika if using. Spread in a single layer on a parchment-lined baking sheet.

Cook

For oven fries: roast for 25–30 minutes, flipping once, until golden and crisp. For stovetop: heat 1/4" vegetable oil in a heavy skillet over medium-high and fry in batches until golden, then drain on paper towels and season immediately with salt. Keep warm until serving.

Tortillas & Assembly

Warm Tortillas

Warm corn tortillas on a hot dry skillet or comal 20–30 seconds per side until pliable and lightly charred. Brush with a little olive oil if you prefer richer flavor. Keep wrapped in a clean towel to stay warm.

Assemble Tacos

Place a small handful (about 2–3 tbsp) of shredded cabbage on each warm tortilla. Top with 2–3 strips of the cooked fish, a spoonful of marinated tomatoes, and 1–2 tablespoons of roasted tomatillo sauce. Sprinkle about 1 tablespoon crumbled feta over each taco. Finish with a squeeze of lime. Serve immediately with fries on the side.