Adjust rack to top position and preheat oven to 425 degrees. Wash and dry produce. 

Trim and quarter radishes. Trim and halve Brussels sprouts lengthwise. Trim and halve zucchini lengthwise; cut crosswise into ½-inch-thick half-moons.

Toss radishes, Brussels sprouts, and zucchini on a baking sheet with a large drizzle of oil, salt, and pepper. Roast on top rack until browned and tender, 12-15 minutes. 

While veggies roast, halve lemon; squeeze juice from lemon halves into a small bowl.

In a second small bowl, combine dressing, mayonnaise, yogurt, 1 TBSP lemon juice, and 1 TBSP water (2 TBSP lemon juice and 2 TBSP water for 4 servings).

Massage grain blend in package to separate grains; partially open package. Microwave until warmed through, 1½-2 minutes.

Transfer grain blend to a large bowl. Add a drizzle of olive oil, salt, and pepper; stir to combine. Let cool for 3-5 minutes (this will prevent the arugula from wilting!).

Once grain blend has cooled, add arugula and half the dressing; toss to combine. 

Divide arugula and grain salad between bowls. Top with roasted veggies and drizzle with remaining dressing. Serve.