Prepare chicken breasts by patting dry with paper towel, cutting into even 2-inch pieces, and placing in a large bowl. In a separate bowl, combine all the marinade ingredients: 1/4 cup lemon juice, olive oil, yogurt, finely minced garlic, tomato paste, red wine vinegar, oregano, paprika, ground allspice, and salt and pepper (to taste; about 1 and 1/2 teaspoons salt and 1/4 teaspoon pepper). Whisk until combined and pour over chicken. Stir to generously coat chicken, cover, and chill. Marinate for 2–24 hours.
Tzatziki: After preparing chicken marinade, make this sauce so it can chill and flavors can develop before serving. Grate a cucumber with the large holes of a grater. Line a small bowl with a few paper towels (or a clean kitchen towel) and add grated cucumber on top. Squeeze as much extra moisture from the cucumber as you can (to keep the sauce from being watery). Once drained, place grated cucumber in a medium bowl. Add Greek yogurt, minced garlic, red wine vinegar, 1/2 teaspoon lemon zest, 1 tablespoon lemon juice, olive oil, and salt and pepper to taste (about 1/4 teaspoon salt and a pinch of pepper). Refrigerate until ready to serve. Whisk right before serving.
Preheat grill to medium-high heat (400–450°F on an outdoor grill) and generously oil the grates. Thread the chicken onto metal (or pre-soaked wooden) skewers. Cook on preheated grill until chicken is golden and no longer pink in the center, about 5 minutes per side.
Preheat oven to 400°F. Line a large baking pan with a silicone baking mat or parchment paper. Cut each pita into 8 triangles and arrange evenly on the prepared pan. Drizzle olive oil over the triangles and use a pastry brush to spread the oil evenly onto the pita bread. Flip the bread and repeat. Sprinkle with salt (about 1/4 teaspoon). Bake 10 minutes, flipping the pita bread halfway through. Serve warm with the chicken. For the tomato/cucumber salad, add the halved tomatoes and thinly sliced cucumber halves to a bowl. Drizzle on a little olive oil and sprinkle on some salt and pepper (to taste).
With the back of a spoon, spread hummus onto 4 large plates. Divide cooked quinoa and chicken skewers evenly among the plates. Top with tomato/cucumber, and drizzle even parts of tzatziki sauce over (or serve on the side). Divide the pita chips. Season individual plates with salt, pepper, and lemon juice as needed. Serve immediately.
Notes
Note 1: to cook the quinoa, add quinoa, broth or water, and 1/2 teaspoon fine sea salt in a small pot. Bring to a boil, then reduce heat to low and cover the pot. Simmer for 10–15 minutes or until all the broth/water is absorbed. Remove from heat, keep the pot covered, and let stand 5–10 minutes. Remove lid and fluff with a fork.Recipe adapted from AllRecipes.Storage: Store leftover skewers and quinoa in separate airtight containers in the fridge. Keep hummus and tzatziki in small containers to avoid mixing flavors. For the freshest taste, consume within 3 days.