Bring a large saucepan of lightly salted water to a boil over high heat. Add sweet and russet potatoes and cook until just tender, about 5 minutes. Drain.
Heat the olive oil in a large skillet (preferably cast-iron) over medium heat. Add Canadian bacon and cook, stirring occasionally, until just starting to brown, 4 to 5 minutes.
Add garlic and cook for 1 minute, stirring frequently.
Add red chile flakes, red bell pepper, and white and light green parts of green onion. Cook until red bell pepper starts to soften, about 2 minutes.
Stir in cooked sweet and russet potatoes, salt, nutmeg and sage. Increase heat to medium-high and cook, stirring occasionally, until the potatoes start to brown, 7 to 8 minutes. Serve.