Preheat your oven to 400°F and line a large baking sheet with parchment paper for easy cleanup.
Chop the sweet potato into 1/2-inch cubes, slice the bell pepper into strips, and break the broccoli into bite-sized florets.
In a large bowl, toss the vegetables with 1 tablespoon of olive oil, 0.25 teaspoon salt, 0.125 teaspoon pepper, and 0.25 teaspoon oregano.
Spread the vegetables in a single layer on the baking sheet and roast for 25 minutes until the sweet potatoes are tender and lightly browned.
While vegetables roast, season the chicken breast evenly on both sides with the remaining salt, pepper, garlic powder, and oregano.
Heat the remaining 0.5 tablespoon of olive oil in a stainless steel or cast-iron skillet over medium-high heat.
Place the chicken in the hot pan and sear for 6 to 8 minutes per side until golden brown and cooked through to an internal temperature of 165°F.
Remove the chicken from the pan and let it rest for 5 minutes before slicing it against the grain.
Plate the roasted vegetables alongside the sliced chicken, top with fresh avocado slices, and finish with a bright squeeze of lemon juice.