Heat a large skillet over medium-high heat. Add the olive oil and butter.
Add the frozen green beans directly to the hot skillet. No thawing is necessary.
Cook for 5–8 minutes, stirring occasionally, until most of the excess moisture has evaporated and the beans begin to develop lightly browned edges.
Add the minced garlic, salt, black pepper, and onion powder. Cook for another 1–2 minutes, stirring frequently.
Remove the skillet from the heat and sprinkle the Parmesan over the green beans.
Add the lemon juice and optional parsley, then toss gently to coat.
Serve immediately while warm.