Preheat oven to 425°. Toss together first 7 ingredients in a 15- x 10-inch jelly-roll pan. Drizzle with 2 Tbsp. olive oil, and sprinkle with 1/2 tsp. salt; toss to coat. Bake 25 minutes or until lightly browned, stirring occasionally. Cool to room temperature (about 30 minutes).
Meanwhile, cook all seeds in a small skillet over medium-low heat, stirring constantly, 4 to 5 minutes or until toasted. Remove from heat; cool completely (about 15 minutes).
Cut avocado into slices, and toss with lemon juice.
Squeeze juice from roasted lemon and orange halves into a large bowl; stir in vinegar and remaining 1/2 tsp. salt. Slowly whisk in remaining 6 Tbsp. olive oil until blended; reserve half of dressing. Toss carrots, salad greens, and red onion with remaining dressing in bowl. Arrange greens on a serving platter or individual plates; top with avocado. Drizzle with crema; sprinkle with toasted seeds. Serve with reserved dressing.
Brought to the table by Elizabeth Winslow, co-founder of Farmhouse Delivery.