Heat the oil in a large saucepan over a medium heat. Add the garlic, fennel and nigella seeds, paprika and turmeric, and stir-fry for 1 minute until fragrant.
Add the watermelon and stir-fry for 4–5 minutes. Remove from the heat, season to taste and add the lime juice and pumpkin seeds. Toss to mix well and serve immediately with the mint scattered over the top.