Preheat the oven to 325°F. Pat the chuck roast chunks dry with paper towels and season evenly with salt and black pepper on all sides.
Heat avocado oil in a Dutch oven over medium-high heat. Add the beef in a single layer, working in batches if needed, and sear for 2-3 minutes per side until deeply browned. Transfer to a plate and set aside.
Reduce the heat to medium and add the sliced onion to the Dutch oven. Cook for 3-4 minutes until softened. Stir in the garlic, ginger, and red curry paste, cooking for another 1-2 minutes until fragrant, stirring frequently to prevent burning.
Pour in the coconut milk and beef broth, scraping up any browned bits from the bottom of the pot. Stir in the soy sauce, brown sugar, and red pepper flakes, if using, until everything is well combined.
Return the seared beef and any accumulated juices to the Dutch oven, making sure the beef is mostly submerged in the coconut sauce. Bring to a gentle simmer, then cover with a tight-fitting lid and transfer to the oven. Braise for 1 1/2–2 1/2 hours, or until the beef is fork-tender. Start checking around 90 minutes, as cooking time will depend on the size of the chunks.
Remove the Dutch oven from the oven and stir in the lime juice. Taste and adjust the seasoning as needed. If you'd prefer a slightly thicker sauce, simmer uncovered on the stovetop for 5–10 minutes until reduced to your liking.
Spoon the tender coconut braised beef over warm jasmine rice, making sure to add plenty of the coconut sauce. Finish with fresh cilantro, sliced green onions, and lime wedges. Add thinly sliced mini bell pepper for a little extra crunch, if desired.