Mix the chicken breast fillet with the sunflower oil, garlic, salt, pepper and thyme and fry in a non-stick pan until crispy. Keep warm.
Bake the pita bread according to the instructions.
Mix yogurt with 2/3 of the lemon juice, salt and pepper (if you like, you can also add 1 pressed garlic clove)
Mix the cucumber, tomatoes, bell pepper, iceberg lettuce and spring onions together. Make a dressing from the balsamic vinegar, olive oil mustard, remaining lemon juice, sugar, salt and pepper and mix with the vegetables.
Cut the warm pita bread in half and fill with the chicken breast, lettuce and yogurt sauce.