Heat the oven to 450 F (230 C). Toss the potatoes with 2 tablespoons oil and half the salt. Spread on a baking sheet.
Bake for 30 to 40 minutes, turning once, until browned and crisp at the edges.
Cook the Chicken:
Toss the chicken with shawarma spice and remaining salt. Heat the remaining oil in a skillet and cook the chicken in batches for 7 to 9 minutes until browned and cooked through.
Mix the yogurt, mayonnaise, garlic, and lemon juice for the garlic sauce.
Assemble:
Divide fries among ovenproof trays, add chicken, and cover with Gouda. Broil for 2 to 4 minutes until the cheese melts.
Top with lettuce, tomato, and cucumber. Drizzle with garlic sauce and sambal and serve at once.
Notes
Keep the broiler-safe trays at least 6 inches from the heat source.