Adjust oven racks to the upper and lower third positions; preheat oven to 450°F
In a medium bowl, toss chickpeas with 2 tablespoons oil, the cumin, coriander, cayenne and 1/2 teaspoon salt. Spread in a single layer on a baking sheet, and top with 3 thyme sprigs. On a separate sheet pan, toss the vegetables with 2 tablespoons oil and 1/2 teaspoon salt. Spread out vegetables in a single layer, and then top with the remaining thyme sprigs.
Set chickpeas on the bottom oven rack, and vegetables on the top. Roast for 10 minutes. Then reverse the pans so the chickpeas are on the top rack. Roast chickpeas for 5 minutes, and roast vegetables for 10 minutes. (If vegetables refuse to color, place them under the broiler for 1 or 2 minutes.) Discard thyme sprigs.
While the veggies and chickpeas roast, make the dressing: Whisk the remaining 1/4 cup oil, the lemon juice, garlic, and a sprinkling of salt and pepper in a small(ish) bowl.
Arrange a layer of brown rice on a platter. Top the rice with the roasted vegetables and half the dressing. Top with the roasted chickpeas, herbs, and the remaining dressing. Serve hot or warm. Take a bow.