Prepare Raita: Drain excess liquid from cucumber and blot with paper towel. In medium bowl, mix together yogurt, cucumber, mint, onion, if using, and cumin. Cover and refrigerate for 1 hour or up to 1 day. To serve, garnish with additional chopped cucumber and paprika, if desired.
Heat oil in a large non-stick skillet over medium heat. Add onion; cook, stirring occasionally, for 6 minutes or until soft. Stir in garlic, ginger and green chile; cook for 1 minute, stirring often.
Stir in tomatoes and ground round, breaking up with a spoon. Stir in coriander and cumin. Cook, stirring, for 2 minutes. Stir in peas. Cover, reduce heat and cook for 5 minutes.
Stir in lemon juice, garam masala and dried chile peppers, if desired. Before serving, stir in fresh coriander. Serve with basmati rice and Raita.