Preheat the oven to 400°F (200°C).
Toss the cauliflower florets with 3 tablespoons of olive oil, the minced garlic, 1 teaspoon kosher salt, and 1/2 teaspoon black pepper in a bowl until evenly coated.
Spread the cauliflower in a single layer on a large baking sheet and roast until tender and lightly charred, about 20–25 minutes. Remove and let cool.
Meanwhile, bring a large pot of salted water to a boil and cook the orzo until al dente according to package directions. Drain in a colander, rinse under cold water, drain well, and toss with the remaining 1 tablespoon olive oil.
In a large bowl, whisk together 3 tablespoons extra-virgin olive oil, 3 tablespoons fresh lemon juice, 1 teaspoon honey, 1 teaspoon Dijon mustard, and salt and pepper to taste to make the dressing.
Add the cooked orzo, roasted cauliflower, thinly sliced red onion, crumbled feta, and dried cherries to the bowl with the dressing; toss until everything is well coated.
Fold in the baby spinach and toss gently until the spinach wilts slightly from the residual heat. Taste and adjust seasoning with additional salt and pepper if desired, then serve.