Preheat your oven to 400°F and line a large baking sheet with parchment paper for easy cleanup.
Toss the diced sweet potatoes on the baking sheet with 0.25 tbsp of the olive oil, a pinch of sea salt, and a pinch of black pepper.
Spread the potatoes in a single layer and roast for 20-25 minutes, flipping halfway through, until they are tender and caramelized on the edges.
While the potatoes roast, whisk together the lemon juice, minced garlic, dried oregano, and the remaining 0.5 tbsp of olive oil in a small bowl.
Place the chicken breast in a shallow dish and pour half of the lemon-herb mixture over it, turning to coat, and let it marinate for at least 10 minutes.
Heat a non-stick skillet over medium-high heat and sear the chicken for 6-7 minutes per side until golden brown and the internal temperature reaches 165°F.
While the chicken is finishing, steam the broccoli florets in a steamer basket for 4-5 minutes until they are bright green and tender-crisp.
Slice the chicken into strips and serve alongside the roasted sweet potatoes and steamed broccoli, drizzling the remaining lemon-herb dressing over the top.