In a small bowl, whisk together tahini paste, water, lemon juice, minced garlic, and salt until smooth and creamy. Adjust the consistency by adding more water if needed to achieve desired thickness. Taste and adjust seasoning, adding more salt or lemon juice if desired.
In a large bowl, combine diced tomatoes, cucumbers, sweet pepper, mint, parsley, and radishes.
Add ½ to 1 cup of prepared tahini sauce, adjusting according to desired consistency.
Sprinkle sumac over the salad for an extra burst of flavour, if desired. Season with salt to taste.
Gently toss all ingredients until well combined.
Serve alongside grilled or roasted white fish for a delightful seafood pairing, or enjoy with rice and roasted vegetables for a satisfying vegetarian option.