In a mixing bowl, combine the gluten-free flour, salt, and cumin seeds. Add the oil and mix until crumbly.
Gradually add water to form a smooth dough. Cover and let it rest for 15-20 minutes.
While the dough rests, prepare the filling by combining mashed sweet potatoes, peas, turmeric, chili powder, garam masala, coriander powder, lemon juice, and black pepper in a bowl. Mix well.
Divide the dough into equal-sized balls, then roll each ball into a thin circle.
Cut the circle in half to create two semi-circles. Form a cone by folding one semi-circle and sealing the edge with a little water.
Fill the cone with about a tablespoon of the sweet potato filling and seal the top by pressing the edges together. Repeat with remaining dough and filling.
Preheat the oven to 400°F (200°C). Place the samosas on a baking sheet lined with parchment paper and brush them with oil.
Bake for 25-30 minutes or until golden brown and crispy, turning halfway through.
Serve warm with your favorite chutney or dipping sauce.