Set a wire rack over a baking sheet or line a plate with paper towels. In a medium bowl, mix the well-drained tuna, parsley, onion, capers if using, harissa if using, salt, and pepper. In a separate small bowl, beat the eggs until evenly blended.

Work with one wrapper at a time, keeping the remaining wrappers covered with a barely damp clean towel so they do not dry out. Place the wrapper on a clean, dry work surface. Spoon about 1 tablespoon of tuna mixture slightly below the center, then spoon about 1 tablespoon of beaten egg over the tuna. Do not overfill.

Fold the bottom corner over the filling, fold in the two side corners, and continue folding into a compact triangle or envelope. Lightly dampen the final edge with water and press to seal. Place seam-side down on a plate. Repeat with the remaining wrappers and filling.

Pour the oil into a large skillet to a depth of about 1/4 inch. Heat over medium to medium-high heat until the oil shimmers; a small scrap of wrapper should sizzle steadily when added. Fry 2 briks at a time, seam-side down first, for 2 to 3 minutes per side, until deep golden and crisp. Adjust the heat as needed so the pastry browns without burning.

Transfer the cooked briks to the prepared rack or paper towels. Let them rest briefly, then serve hot with lemon wedges. The egg filling should be fully set before serving.