Step 1

Preheat oven to 425°. Bring a medium saucepan of salted water to a boil; add lentils. Adjust heat and simmer until just cooked through, 25–30 minutes. Drain lentils and transfer to a large bowl; let cool slightly.

Step 2

Meanwhile, whisk coriander, 3 Tbsp. oil, 1 Tbsp. harissa paste, 2 tsp. salt, and ½ tsp. pepper in a small bowl. Arrange sweet potatoes and tomatoes on a rimmed baking sheet and drizzle with harissa oil (reserve bowl for dressing). Roast, tossing once, until sweet potatoes are tender and browned on some sides and tomatoes burst, 25–30 minutes.

Step 3

Whisk vinegar, honey, and remaining 1 Tbsp. harissa in reserved bowl. Stream in remaining 4 Tbsp. oil, whisking constantly until emulsified; season vinaigrette with salt.

Step 4

Add half of vinaigrette to lentils and toss to combine. Taste and season with salt and pepper. Divide among bowls. Top with roasted vegetables and cilantro. Drizzle with remaining vinaigrette.

Step 5

Do Ahead: Lentils can be cooked 3 days ahead. Let cool; cover and chill.