2 teaspoons fresh lemon juice1 teaspoon olive oil1/2 teaspoon dried hot chili flakes1 small garlic clove, crushed1 (about 130g) chicken thigh fillet, excess fat trimmed1 tablespoon good-quality whole-egg mayonnaise1/4 teaspoon crushed garlic, extra1 crusty bread roll or bun, split2 baby lettuce leaves, washed, dried1 small ripe tomato, thinly sliced