Prep and measure everything: have the cooked lentils, roasted sweet potato cubes, arugula, crumbled feta and toasted walnuts nearby. Finely mince the shallot and garlic. Mise en place saves time and helps you balance flavors as you taste.

Warm a medium nonstick skillet over medium heat and add 1 tsp olive oil. Add the minced shallot and sauté for 30–45 seconds until translucent — this softens the shallot and tames its sharpness so it melds with the dressing. Add the minced garlic and cook 15–20 seconds more until fragrant; don't brown it or it will taste bitter.

Add the cooked lentils to the skillet and spread into an even layer. Let them sit undisturbed for 1–2 minutes, then gently stir and cook another 1–2 minutes until just warmed through. Warming the lentils helps them absorb flavors from the warm dressing and keeps the salad comforting rather than cold and listless.

Push the lentils to one side of the skillet and add the roasted sweet potato cubes in a single layer. If the sweet potatoes were roasted ahead and refrigerated, sear them for 2–3 minutes per side to revive crisp caramelized edges — this contrasts beautifully with the soft interior and intensifies sweetness. If they’re already hot, just toss them with the lentils to warm through.

While the lentils and sweet potato warm, whisk the dressing: in a small bowl combine 1 tbsp extra-virgin olive oil, 1 tbsp balsamic vinegar, 1 tsp Dijon mustard, 1 tsp honey (optional) and a pinch of salt and pepper. Whisk until emulsified. Making and tasting the dressing now allows you to adjust acidity and sweetness to the warmed vegetables' flavors.

Pour the warm dressing into the skillet, tossing gently to coat the lentils and sweet potato. Heat helps the oil bloom the aromatics and lets the balsamic slightly reduce and cling to the surfaces, creating a glossy coating. Taste and adjust seasoning: add a pinch more salt, a grind of black pepper, or 1/2 tsp lemon juice if you want additional brightness.

Arrange the arugula or mixed greens on two plates (or one shallow platter) and top with the warm lentil–sweet potato mixture. Tossing warm ingredients with the greens right before serving slightly wilts the leaves for better texture and mouthfeel while retaining fresh peppery notes.

Scatter the crumbled feta and toasted walnuts over the top. The salty tang of feta and the crunchy, bitter-sweet walnuts provide contrast in both flavor and texture — this interplay makes the salad memorable.

Finish with a final drizzle of any remaining dressing, a small squeeze of lemon if desired, and a light crack of freshly ground black pepper. Serve immediately so the warm and cool elements are at their best.

Optional plating flourish: press a few of the sweet potato cubes on top, sprinkle a few whole walnut halves for visual height, and add a tiny basil or parsley leaf for color. This elevates the presentation for a restaurant-quality finish.