Halve peppers lengthwise through the stems, leaving the stems attached.
Remove the seeds and white membrane. Place the peppers cut-side down in a large microwave-safe dish. Add 1/2 inch water, cover, and microwave on high until the peppers are just softened, 7-9 minutes. Let cool slightly, drain and set aside.
Meanwhile, bring a large saucepan of water to a boil. Add orzo and cook until just tender, 8-10 minutes or according to package directions. Drain and rinse with cold water.
Mash chickpeas into a chunky paste with a fork, leaving some whole.
Heat oil in a large nonstick skillet over medium heat. Add onion and cook, stirring, until soft, about 4 minutes. Add spinach and oregano and cook, stirring, until the spinach is wilted, about 1 minute. Stir in the orzo, chickpeas, 1/2 C Feta cheese, tomatoes, vinegar and salt. Cook until heated though, about 1 minute. Divide the filling among the pepper halves and sprinkle each pepper with some of the remaining 1/4 C Feta.