Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper.
Toss the cauliflower florets with olive oil, salt, and pepper. Spread them in a single layer on the prepared baking sheet - do not crowd them.
Roast for 20 to 25 minutes, flipping halfway through, until the florets are tender inside and golden-brown on the edges.
While the cauliflower roasts, make the sauce. Combine honey, soy sauce, rice vinegar, sesame oil, garlic, ginger, and red pepper flakes in a small saucepan.
Heat over medium heat, stirring constantly, until the sauce simmers and thickens slightly - about 3 to 5 minutes. Remove from heat.
Transfer the roasted cauliflower to a large bowl. Pour the warm sauce over the top and toss gently until every floret is fully coated.
Serve immediately, garnished generously with sesame seeds and chopped green onions.