Build the Aromatic Foundation: In a large Dutch oven or heavy-bottomed pot, warm 3 tablespoons of extra virgin olive oil over medium heat. Add the chopped onion and sliced leek, stirring occasionally until they soften and become translucent, about 6-8 minutes. Add the minced garlic and cook for another minute until fragrant, being careful not to brown it.
Infuse the Herbs & Spices: Stir the tomato paste into the aromatic base and cook for 1 minute to deepen its flavor. Add the dried spearmint, chopped dill, black pepper, and optional red pepper flakes. Stir continuously for 30 seconds to toast the spices and release their essential oils.
Integrate the Liquid & Grain: Add the uncooked brown rice to the pot and stir to coat each grain with the seasoned oil. Pour in the low-sodium vegetable broth and bring the mixture to a gentle boil.
Hydrate the Rice: Once boiling, reduce the heat to low, cover the pot tightly, and let the rice simmer for 25 minutes. Do not lift the lid during this time. The rice will be partially cooked.
Wilt the Spinach: Uncover the pot. Add the fresh spinach in large handfuls, stirring it into the rice mixture as it wilts. You may need to do this in 3-4 batches. Once all the spinach is incorporated, replace the lid and continue to simmer for another 10-15 minutes, or until the rice is tender and has absorbed most of the liquid.
Finish with Acidity & Enrichment: Remove the pot from the heat. Stir in the fresh lemon juice and lemon zest. Drizzle with the remaining 2 tablespoons of finishing olive oil. Fluff gently with a fork and let it rest for 5 minutes before serving. Garnish with additional fresh dill.