Place diced sweet potatoes on a parchment-lined baking sheet. Drizzle with 1-2 tbsp olive or avocado oil and stir until potatoes are evenly coated. Roast for 20-30 minutes checking every 5-10 minutes to stir. Remove from the oven when they are tender and slightly toasted.
While sweet potatoes are cooking, dice swiss chard and mushrooms. Be sure the separate the stems of the swiss chard from the greens.
Saute the swiss chard stems with 1-2 tbsp olive oil in a medium frying pan over medium-high heat for 3-4 minutes. Add swiss chard greens, mushrooms, and seasonings. Continue to cook for 3-4 more minutes until greens are slightly wilted and mushrooms are tender. Remove from heat.
Remove sweet potatoes from the oven and add to the frying pan with the swiss chard and mushrooms. Mix together and serve with diced avocado on top.