Preheat the oven. Arrange a rack in the middle of the oven. Heat the oven to 400ºF/204ºC.
Roast the peppers and the aromatics. Sprinkle the bell peppers, quartered onion and garlic cloves with salt, drizzle with olive oil, and arrange them in a single layer on a baking sheet. Make sure you have a large enough baking sheet (use two sheets if necessary), so the vegetables aren't too crowded and don't steam instead of roasting. Roast the bell peppers and aromatics until caramelized and slightly blackened, 25-30 minutes.
Peel the peppers (optional, depending on the peppers). Thin-skinned bell peppers don't need to be peeled. If you're using thick-skinned peppers, let the roasted peppers cool for a few minutes until comfortable enough to handle. Then peel the skins off and discard them. The skins will slip off easily.
Blend. Add the roasted bell peppers, roasted aromatics, sun-dried tomatoes, vegetable broth, lemon juice, and salt into a high-speed blender and blend on high until completely smooth. Once blended, the soup will take on a deep red-orange hue and silky-smooth texture.
Season. Taste and adjust the flavor as needed, adding more salt for saltiness and lemon juice for acidity. If the soup is not sweet enough, you can add a little bit of maple syrup.
Serve. Pour the soup into serving bowls - it will be hot straight out of the blender (if using Vitamix). Garnish with a drizzle of cashew cream and a sprinkle of black pepper.
Store. Leftover soup keeps well covered in the refrigerator for 3-4 days. For longer term storage, freeze in an airtight container for up to 3 months.
Reheat. Transfer frozen soup into the refrigerator 24 hours before reheating to thaw slightly. Reheat in a pot on the stovetop over medium-low heat, stirring frequently, until hot. Add ¼ cup/60 ml water/broth at a time if too thick.