Heat a large non-stick skillet over high heat. While the pan is heating, set an empty sheet pan next to the stove.
Lightly spray the hot skillet with canola oil, then add a single layer of green beans (about half of the bag). Allow them to blister in the pan without disturbing them, for 2 to 3 minutes. Then shake the skillet to char on all sides. Transfer blistered beans to the sheet pan. Repeat with remaining green beans.
After the final batch of green beans has been transferred to the sheet pan, spray the empty skillet with more canola oil, then add the red onion slices, tossing them occasionally until they begin to char on the edges, 2-3 minutes.
Add all of the green beans back to the skillet with the onions, and add the chopped garlic, tossing to combine.
Season with salt, add the sweet chili sauce, then toss to coat.
Sprinkle in the chopped almonds, reserving a handful for garnish.
Place green beans on a platter and garnish with the remaining almonds to serve.