Preheat oven to 425 degrees F.On a large rimmed baking sheet, combine the cauliflower, chickpeas, olive oil, chili powder, paprika, garlic, crushed red pepper flakes, and a pinch each of salt and pepper. Toss well to evenly coat. Transfer to the oven and roast for 20 minutes, or until tender and lightly charred.Meanwhile, in a large salad bowl, combine the mixed greens, cucumbers, herbs, and chives.To make the vinaigrette. Combine all ingredients in a glass jar or measuring cup and shake (or whisk) until completely smooth. Taste and adjust the salt and pepper.Toss the roasted cauliflower and chickpeas in with the salad. Add a little of the vinaigrette and toss to combine. Top the salad with avocado and feta cheese. Serve and enjoy! The salad keeps well for 3-4 days in the fridge, add the vinaigrette just before serving.