Heat oil in a medium skillet; add shrimp and sauté over high heat, stirring, until pink and tender, about 3 minutes.
Stir in scallion and garlic; add tomato and sprinkle with oregano. Cover and set aside.
Meanwhile, cook the pasta in plenty of boiling salted water until al dente, about 10 minutes. Add ¼ of the pasta water to the shrimp mixture. Drain pasta.
Toss pasta, shrimp mixture and peas. Season with salt and pepper to taste.