Preheat your oven to 425º F and arrange a rack in the center of the oven.
Add the drained mackerel, peppers, onions, Greek yogurt, cumin, chili powder, shredded cheese, and salt to a large mixing bowl, and mix until all of the ingredients are well blended.
Line a baking sheet with parchment paper and lightly brush some olive oil over the parchment.Place a large tortilla onto the parchment and scoop half of the filling onto one side of the tortilla. Pat the filling down a bit to secure, and fold the tortilla over, pressing down lightly. Carefully slide the tortilla to one side of the baking sheet and place the other tortilla down. Repeat the same steps for filling and folding.
Lightly brush the tops of the folded tortillas with olive oil.Place in the oven on the center rack and bake for about 15 minutes, or until the tortillas are lightly golden and crisped.
When done, remove from the oven and let them sit for about 5 minutes to cool a bit.
Cut the tortillas into wedges, place on a serving platter, and serve with salsa, guacamole, and plain Greek yogurt (or sour cream).