Bring a medium sauce pot of water to a boil. Add the rice noodles and cook until just tender, 4 to 5 minutes. Drain and rinse with cold water; set aside. Wipe out the pot.
While the noodles cook, prepare the pork floss.

• Transfer the braised pork to a large bowl; using your hands or a fork, separate the meat into very thin strands. Season with salt and pepper.

Working in batches if needed, in a dry large frying pan over medium-high heat, spread the pork in an even layer and cook until starting to brown on one side, about 1 minute. Reduce the heat to medium-low and continue cooking, turning once halfway through, until lightly browned and crisp on the outside and chewy within, 10 to 12 minutes. [Return all the pork to the pan.] Remove from the heat and stir in as much sambal oelek as you like.
While the pork cooks, prepare the coconut broth.

• Peel and thinly slice enough onion to measure ¾ cup [1½ cups].

In the same pot used for the noodles, warm 1 to 2 teaspoons [1 TBL] oil over medium-high heat until hot but not smoking. Add the onion, season with salt and pepper, and cook, stirring occasionally, until starting to soften, 2 to 4 minutes. Stir in the khao soi curry paste and cook until fragrant, about 1 minute.
Stir in the coconut milk and ¼ cup [½ cup] water. Bring to a boil, reduce to a simmer, and cook until the broth is thickened slightly, 1 to 3 minutes. Working in batches if needed, stir in the spinach and cook until just wilted, 1 to 2 minutes. Remove from the heat and season to taste with salt and pepper.
While the broth simmers, prepare the garnishes.

• Cut the lemon into wedges.
• Remove any coarse stems from the cilantro sprigs.

Transfer the coconut broth to individual bowls, add the rice noodles, and top with the pork floss. Garnish with the cilantro and serve with the lemon wedges.