Prep the vegetables: slice the Cucumber and Carrot into thin matchsticks, thinly shred the Green cabbage, trim and cut the Yardlong beans into 1–2 inch pieces, and core and cut the Pineapple into small bite-sized chunks. Place them in a large bowl and sprinkle with Coarse salt; toss and let sit 15–20 minutes to draw out excess water.
Rinse and drain: After the vegetables have wilted slightly, rinse them briefly under cold water to remove excess salt, then gently squeeze or spin dry and return to the bowl.
Prepare the spice components: remove stems/seeds as desired from the Dried red chilies. Peel the Shallots and Garlic; take the tender inner stalk of the Lemongrass and thinly slice it, then roughly chop the Fresh galangal and Fresh turmeric.
Toast and grind (or blend): lightly toast the Candlenuts and the Dried red chilies in a dry pan until fragrant (watch closely so they don’t burn). Grind or pulse together the toasted items with the prepared shallots, garlic, lemongrass, galangal and turmeric until you have a coarse paste. Add the Belacan (shrimp paste) and pulse briefly to combine.
Cook the paste: heat 1–2 tablespoons of Neutral oil in a small pan over medium heat, then sauté the spice paste until fragrant and the raw edge has cooked off, about 3–5 minutes.
Make the pickling liquid: stir in Rice vinegar, Sugar and a pinch of Fine salt to the warm paste; simmer gently for 1–2 minutes until sugar dissolves. Taste and adjust sweetness or tang to your preference.
Combine and marinate: pour the warm pickling sauce over the prepared vegetables and Pineapple, tossing thoroughly so everything is evenly coated. Let cool to room temperature, then refrigerate for at least 1–2 hours (or overnight) to allow flavors to meld.
Finish and serve: just before serving, scatter chopped or crushed Roasted peanuts and a sprinkle of Sesame seeds over the acar for crunch and a nutty finish. Serve chilled or at cool room temperature as a bright, tangy side.
