Preheat your oven to 400°F and line a small baking sheet with parchment paper.
Toss the cubed red potatoes with the olive oil, salt, and pepper, then spread them in a single layer on the baking sheet.
Roast the potatoes for 20-25 minutes, flipping halfway through, until they are golden brown and crisp.
While the potatoes roast, season the lamb leg with dried oregano, salt, and pepper.
Grill the lamb over medium-high heat for approximately 4-5 minutes per side, or until it reaches an internal temperature of 145°F for medium-rare.
Remove the lamb from the grill and let it rest for 5 minutes before slicing it into thin strips against the grain.
In a large mixing bowl, whisk together the lemon juice, minced garlic, and fresh mint to create the dressing.
Add the arugula, sliced red bell peppers, and roasted potatoes to the bowl, tossing gently to coat with the dressing.
Top the salad with the sliced grilled lamb and serve immediately while the potatoes and meat are still warm.