Preheat the broiler on high. Line a rimmed baking sheet with aluminum foil.
Pulse 1/3 cup of the pita chips in a food processor until finely ground. Transfer to a large bowl and drizzle with 1 tablespoon each of the red wine vinegar and olive oil.
Coarsely chop one of the onion halves and add it to the food processor along with the garlic and 1/4 cup of the parsley; 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 black 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 ball. Place the meatballs on the prepared baking sheet, spacing them about 1 inch apart.
Broil until the meatballs are cooked through, about 4 minutes. Let cool slightly.
Meanwhile, thinly slice the remaining red onion half. Coarsely crush the remaining 1 cup pita chips.
Whisk together the yogurt and remaining 4 tablespoons red wine vinegar and 1 tablespoon olive oil in a large bowl. Add the sliced onions, tomatoes, feta, romaine, cucumber, bell pepper, 1/4 teaspoon salt, a few grinds of pepper and the remaining 1/4 cup parsley. Toss to combine. Adjust the seasoning with salt as needed.
Divide the salad among 4 plates. Top each with some meatballs and the crushed pita chips.