Make the cilantro-lime vinaigrette by combining lime juice, honey, minced garlic, 1/4 cup cilantro, 1/4 teaspoon salt, 1/4 teaspoon pepper, pinch of red pepper flakes, and 1/3 cup olive oil in a blender or food processor; blend until smooth or mostly smooth. Chill if making ahead.
Preheat the grill to high and let it heat for about 10 minutes.
Bring a large pot of salted water to a boil and cook the orzo according to package directions; drain and transfer to a large bowl.
Season the chicken breasts all over with smoked paprika, garlic powder, and a generous pinch of kosher salt and black pepper.
Grill the chicken 5 minutes per side, or until an instant-read thermometer reads 165°F (74°C). Remove from the grill and let rest 10 minutes, then slice or chop.
Toss the cooked orzo with half of the cilantro-lime vinaigrette, then stir in the sliced green onions and the handful of chopped cilantro.
Add the sliced or chopped grilled chicken to the orzo and gently toss to combine.
If serving immediately, fold in the cubed avocado and drizzle additional dressing as desired; serve warm or at room temperature.