In a pan, dry roast coriander seeds, cumin seeds, fennel seeds, and black pepper on low flame. Transfer to a plate and let them cool slightly.
Grind the roasted spices into a coarse powder using a grinder or food processor. Set aside.
In another pan, heat oil and sauté chopped ginger and green chili.
Add the coarsely ground spice mixture and sauté.
Mix in boiled and roughly mashed potatoes, green peas, coriander powder, red chili powder, garam masala, amchur powder, salt, and chopped coriander leaves. Stir well to combine.
Your samosa stuffing is now ready.