First, brown your sausage in a large skillet. If it's in casings (like a bratwurst), remove those first. Once it's almost all the way cooked, remove it from the pan and drain off some of the drippings (or save for another use.) Turn your oven to 375.
Get out your food processor. This can also be done by hand, but the grating/shredding blade on your processor makes very quick work of everything.
I'd recommend first grating your cheese and setting it aside. It's going to be mixed in with the cream and eggs in a bit.
After you've grated your cheese, give your processor a quick swipe to clean away any remaining cheese, and get started on the potatoes. Using a relatively fine shredder blade, shred all your potatoes. You're going for 4-6 cups, total. Place the shredded potatoes in a large mixing bowl.
Next up, green bell peppers or blanched broccoli (just 2-3 minutes in boiling water then drained and into ice water.) If using green peppers, first remove the stems, the white ribs and any seeds on the inside. Into the processor they go! Add the shredded peppers to the potatoes.
Next up, the greens-- and depending on how tough they are, they might also benefit from a quick blanch (or a sauté in the drippings pan from the sausage) for just a minute or two. If you're going to sauté or blanch the kale, just mince it finely with a knife rather than gumming it ip in the processor. If you're going to use it raw (tastes great, too), just use the processor like the rest of the veggies.
Stir the kale, peppers and potatoes together well.
In a separate mixing bowl, add your eggs, your milk or heavy cream, the minced fresh herbs, some salt and pepper, the red pepper flakes, and about 2/3rds of the grated cheese. Mix well.
For easier clean-up, you can line your baking dish with parchment paper, and the brush it with your 1 tbsp oil. You can also just grease the pan itself. Mix the eggs/milk/cheese into the potato/pepper/kale, and press into the baking dish. Scatter the remaining cheese over top and cover with foil. Bake for 45 minutes, then remove foil and broil under high for 5-8 more minutes.
Allow to rest for 5 minutes, then slice and serve!