Heat oil in a large nonstick skillet over medium heat. Add sliced onion and sauté until tender and translucent, about 4 minutes. Add garlic, cumin, salt and pepper and cook additional 2 minutes. Add shrimp, stirring frequently and cook until shrimp are pink, about 3 minutes. Reduce heat add diced chipotles and tomatoes and simmer for 5 minutes until sauce thickens a bit. Serve warm over pureed hominy.