Preheat the grill on high. Line a rimmed baking sheet with aluminum foil.
Pulse 1/2 cup of the pita chips in a food processor until finely ground. Transfer to a large bowl and drizzle with 1 tablespoon each red wine vinegar and olive oil.
Coarsely chop one of the onion halves and add it to the food processor. Add 1/4 cup of the mint and the garlic and pulse until very finely chopped. Add this mixture to the bowl with the ground pita chips and mix well with your hands. Add the beef, cinnamon, 1/2 teaspoon salt and 1/4 teaspoon pepper and mix gently with your hands until well combined.
Dampen your hands and form the mixture into 24 small meatballs, using about 1 tablespoon for each. Place on the prepared baking sheet, spacing the meatballs about 1 inch apart. Spread the tomatoes cut-side up in a single layer on the other side of the pan.
Broil until the meatballs are almost cooked through and browned and the tomatoes are blistered, 4 to 5 minutes. Let cool slightly.
Combine the yoghurt, the remaining 4 tablespoons red wine vinegar and the remaining 1 tablespoon olive oil to make the dressing. Very thinly slice the remaining onion half and add it to a clean large bowl along with the lettuce, bell peppers and remaining 1/4 cup mint leaves. Toss with the dressing and 1/8 teaspoon each salt and pepper. Top with the meatballs, tomatoes and remaining 1 cup pita chips and serve.