Preheat your oven to 400°F and line a baking sheet with parchment paper.
Peel and cube the sweet potato into small 1/2-inch pieces, then slice the zucchini into half-moons and chop the red bell pepper.
Toss the sweet potato, zucchini, and bell pepper with 0.25 tbsp of olive oil, half the sea salt, and half the black pepper on the prepared tray.
Roast the vegetables for 20-25 minutes until the sweet potatoes are tender and the edges are slightly caramelized.
While the vegetables roast, heat a skillet over medium-high heat with the remaining 0.25 tbsp of olive oil.
Add the ground beef to the skillet, seasoning with the remaining salt, pepper, and garlic powder, and cook until browned and fully cooked through.
Drain any excess fat from the beef and stir in the cooked lentils to warm them through.
Allow the beef mixture and roasted vegetables to cool completely to room temperature.
Combine the beef, lentils, and roasted vegetables in a bowl, then drizzle with fresh lemon juice.
Store in an airtight container in the refrigerator until ready to serve cold.