Trim kale of ribs and stems and tear them into bite-size pieces.
Heat a large pot or Dutch oven over medium heat. Add chopped bacon and cook until rendered and crisp. Remove to a paper towel-lined plate.
Add enough olive oil to the remaining bacon fat to equal 2 tbsp (you may not need it).
Add sliced onions and cook over medium heat until soft, about 5-7 minutes. Add sliced garlic and chili flakes and continue to cook for an additional 2 minutes.
Toss in trimmed kale and salt and pepper and cook, stirring often until kale is starting to wilt 3-5 minutes.
Pour in broth and water, cover and cook for 12-15 minutes, stirring once or twice until kale is soft. Remove lid and continue to cook for 3-5 minutes until most of the liquid has cooked out.
Add parmesan cheese and bacon and toss to combine. Add a generous squeeze of fresh lemon juice. Serve immediately.