For the sauce, add all ingredients to a food processor and process well for 30 seconds until smooth, scraping down the sides. If sauce seems very thick, add a tablespoon or two of water to thin it out. Set aside.
Cook pasta in salted boiling water until al dente, probably 7-8 minutes. In the last minute, add peas as well. Drain pasta and peas and then rinse with cold water to cool pasta down.
Transfer pasta and peas to a bowl and pour over sauce. Mix well.
Serve pasta salad at room temperature or cold with feta cheese and scallions.