Bring water, wild rice and salt to the boil in a saucepan. Reduce heat to medium-low; cover and simmer until rice is tender, 30 to 45 minutes. Drain excess liquid, fluff rice with a fork and cook uncovered 5 minutes more.
Bring a large pot of lightly salted water to the boil. Cook orzo in the boiling water, stirring occasionally until tender yet firm to the bite, 7 to 10 minutes. Drain.
Melt 1 tablespoon butter in a large nonstick pan over medium heat. Add onions; cover and cook until softened, about 5 minutes. Stir in remaining 2 tablespoons butter, peas, salt and pepper. Cook and stir until combined, about 1 minute more.
Pour rice and orzo into a serving dish. Stir in the pea mixture and chopped spring onions.
This recipe can be made ahead of time and reheated, covered, in the microwave.