In a deep baking tray or casserole dish, combine 1 finely chopped onion, 2 finely chopped garlic cloves, 1 chopped red pepper, and 150g halved baby tomatoes. Stir in the finely grated zest and juice of 1 lemon along with 1 tablespoon of dried oregano. Spray with cooking spray and place in the oven for 15 minutes.
Remove from the oven and mix in 300g dried orzo, a small handful of finely chopped mint leaves, and 50g baby spinach. Season to taste, then pour in 800ml vegetable stock. Stir again and return to the oven for another 15 minutes.
Take the dish out of the oven, stir, and evenly cover the top with 90g feta (cut into chunks). Sprinkle with 2 tablespoons of sunflower seeds.
Bake for an additional 10 minutes, until the orzo is fully cooked with no bite left, the feta is melted and starting to brown, and the sunflower seeds are golden.