Heat oil in frying pan. Add onion, cumin, ginger, turmeric, cardamom, coriander and chilis. Cook gently 5 minutes. Add mashed potatoes and peas. Stir in lime juice. Remove from heat and cool.
Sift flour into bowl. Cut in margarine and mix until resembles fine bread crumbs. Add milk and mix to form a stiff dough.
Divide dough into 6 equal pieces. From the pieces into a ball, and roll our into a 6" circle. Cut each circle in half. Divide filling into 12 portions.
Dampen edges of dough, then fold the straight edge together and squeeze shut, holding it open in your hand fill the cone with filling. Fold over and seal dough to form triangles.
Heat oil in deep fryer or pan, until 375°F. Fry samosa in oil until golden brown 3-4 minutes, turning if needed. Drain on paper towels.