Slice the chicken breast horizontally to make two thinner pieces, then cut each into steak-sized portions for even grilling.

In a bowl, mix olive oil, lemon juice, garlic powder, smoked paprika, salt, and black pepper. Add chicken pieces and coat well. Let marinate for 10 minutes (or up to 1 hour in the fridge for more flavor).

While chicken marinates, prepare the sauce. In a small bowl, combine Greek yogurt and Dijon mustard. Stir until smooth, and season with a pinch of salt and pepper if desired.

Heat grill pan or outdoor grill to medium-high. Grill chicken for 4-5 minutes per side, until well browned and cooked through (internal temperature should reach 75°C/165°F). Remove from heat and rest 2 minutes, then slice chicken into strips.

Warm tortillas on a dry pan or in the microwave until just flexible.

Lay out each tortilla. Spread 2 tablespoons of yogurt sauce down the center. Layer with lettuce, sliced tomato, onion, and sliced grilled chicken. Add optional herbs or cheese if desired.

Fold in the sides and roll up tightly into a wrap. Slice in half to serve.