Pat the tofu cubes dry with paper towels—removing surface moisture is the only way to get a good sear rather than steaming them. Season with salt and pepper.

Heat the vegetable oil in a large Dutch oven over medium-high heat until it shimmers. Add the tofu and cook, turning occasionally, until golden brown on all sides, about 8 to 10 minutes. Transfer the tofu to a plate and set aside.

Add the mushrooms to the empty pot and cook until they have released their liquid and are well-browned, about 5 minutes. Stir in the chili-garlic sauce, garlic, and ginger and cook until the garlic is fragrant.

Pour in the vegetable broth, cider vinegar, soy sauce, and sugar. Bring the liquid to a boil, scraping up any browned bits from the bottom of the pot to incorporate the concentrated flavor into the broth.

Add the ramen noodles to the pot and reduce the heat to medium. Simmer until the noodles are tender, about 3 minutes, using a fork to gently pull the blocks apart as they soften.

Stir the browned tofu and baby spinach into the pot and cook until the spinach is just wilted. Serve immediately in deep bowls while the broth is piping hot and the noodles are perfectly chewy.