Take the tomatoes and with a sharp knife, slice the tops off each tomato. Carefully use a spoon to scoop out the insides, retaining some of the flesh to maintain the tomato shell. Set the scooped insides aside for later use.
In a medium-sized saucepan, pour in the rinsed quinoa and vegetable broth. Bring this mixture to a vigorous boil over high heat. Once boiling, reduce the heat to low, cover the pot, and allow the quinoa to simmer for approximately 15 minutes, or until the grains are fluffy and all the liquid has been absorbed.
While the quinoa is cooking, heat the olive oil in a non-stick skillet over medium heat. Add the finely chopped red onion and diced bell pepper, sautéing for about 5 minutes until both are tender and fragrant.
Once the quinoa has finished cooking, transfer it to a mixing bowl. Add the sautéed onion and bell pepper mixture, diced cucumber, chopped Kalamata olives, crumbled feta cheese, chopped parsley, lemon juice, salt, and freshly ground black pepper. Stir the mixture gently but thoroughly until well combined.
Carefully spoon the quinoa and vegetable mixture into the hollowed-out tomatoes, ensuring to pack the filling down lightly to maximize the stuffing.
Arrange the stuffed tomatoes in a baking dish, then drizzle a little olive oil over the tops of each tomato for added richness.
Place the baking dish in the preheated oven and bake for 20-25 minutes, or until the tomatoes are tender yet still hold their shape.
Once baked, carefully remove the dish from the oven and allow the tomatoes to cool for a few minutes before serving.
Notes
Serve warm on a platter, garnished with additional parsley leaves and drizzled with balsamic glaze.