Green lentils are delicate in flavor and hold their shape during cooking. Brown lentils can be used instead.
In a medium saucepan, bring lentils, garlic, and 2 cups water to a boil over high. Reduce heat and simmer until lentils are tender, about 25 minutes. Season with salt and pepper and let cool.
Preheat oven to 350 degrees. Arrange roasted vegetables in a single layer on a rimmed baking sheet and bake until warmed through, 8 to 10 minutes.
Arrange arugula on a platter and top with vegetables, lentils, and cheese. Drizzle with vinegar and oil and season with salt and pepper.
You can wash and trim the arugula up to 4 days in advance. The lentils can also be prepared in advance and stored in their cooking liquid in an airtight container up to 5 days.