Preheat oven to 400 F. Line baking sheet with parchment paper or silicone mat.
In small bowl, toss radishes with 2 tsp oil and 1/4 tsp salt. Spread out on baking sheet, place in oven, and bake for 30 minutes, or until radishes are wrinkled and tender, stirring once halfway through baking.
Meanwhile, in medium-sized pot, place lentils and add enough water to cover by 2 inches. Bring to a boil; reduce heat to medium-low, and simmer, covered, until lentils are tender, about 25 minutes. Drain well.
In small bowl, whisk together 3 Tbsp oil, vinegar, chives, mustard, red pepper flakes, black pepper, and 1/4 tsp salt.
To serve, divide lettuce, arugula, lentils, radishes, avocado, almonds, and feta among serving plates. Drizzle on chive dressing.