Masala

2 tablespoons vegetable oil
2 cups chopped onions
4 large garlic cloves, minced
1 1/2 teaspoons garam masala
1 1/2 teaspoons curry powder
1 1/2 teaspoons ground coriander
1 teaspoon turmeric
1/2 teaspoon cayenne pepper
1 28-ounce can diced tomatoes in juice
1 cup plain whole-milk yogurt

Shrimp

2 tablespoons vegetable oil
2 pounds uncooked large shrimp, peeled, deveined
1 13 1/2-ounce can unsweetened coconut milk
1/2 cup chopped fresh cilantro
1/4 cup chopped green onion tops
1 1/2 tablespoons fresh lemon juice