Peel and devein the shrimps. Mixed with 1/8 teaspoon of salt and black pepper.
Cut onion into thin wedges. Slice snow peas into 0.5'' thick strips (you can skip this if your snow peas are small enough). Cut red bell pepper into 1'' x 1'' pieces.
Put a pan/skillet over medium - medium high heat. When it's hot, add some oil and red onion. Sauté onion until fragrant, about 2 minutes.
Add red bell pepper and snow peas to the pan, stir-fry for about 2 minutes.
Add mung bean sprouts, 1/8 teaspoon of salt, black pepper and stir-fry for about 1 minute or just until all veggies are 80-90% cooked. Transfer to a plate.
Make sure the pan is hot, add some oil and shrimps. Brown the shrimps for 1-2 minutes.
Add garlic and add all veggies back to the pan. Add oyster sauce, soy sauce and fish sauce and stir to coat everything well in sauces. Stir fry until all ingredients are cooked through.
Garnish with scallion and cilantro. Serve hot with rice.