Heat the olive oil in a large pot or Dutch oven over medium-low heat.
Add the diced onion and celery.
Cook for 5 minutes, stirring occasionally, until the onion becomes translucent.
Stir in the grated ginger and minced garlic, and continue to cook for 5 minutes more, until all the vegetables are soft and fragrant.
Add the sweet potato chunks and the can of diced tomatoes with chiles. Increase the heat to medium and cook for 5 minutes, stirring occasionally, allowing the sauce to thicken slightly.
Pour in 2 cups (480 ml) of water and season generously with salt and pepper.
Bring to a simmer, then partially cover the pot and cook for 10 minutes.
Add the butternut squash and cauliflower florets to the pot.
Stir to combine, return to a simmer, and cook for another 15 minutes, or until all the vegetables are tender when pierced with a fork.
In a small bowl, whisk together the peanut butter and ½ cup of warm water to create a smooth, pourable slurry.
Stir this mixture into the stew.
Continue to cook for 4-5 minutes, stirring constantly, as the stew thickens into a rich, creamy consistency.
Serve hot over brown rice, garnished with fresh watercress.
Stir in a few handfuls of fresh spinach or kale during the last 5 minutes of cooking for an extra boost of nutrients and color.