Heat olive oil in a medium skillet over medium heat. Once hot, add half of the swiss chard leaves, paprika, and cumin. Season generously with Kosher salt and a sprinkling of freshly ground pepper. Once swiss chard leaves begin to wilt and there is enough room in the pan, add in remaining swiss chard and a splash of water. Cook until chard is tender, about 5 minutes.
Meanwhile, in a small bowl whisk eggs thoroughly to incorporate lots of air. Add in heavy cream/whole milk, season liberally with Kosher salt and freshly ground pepper, and whisk until well combined. Add a little dab of butter to a medium nonstick skillet over medium-low heat. Once melted, add eggs, stirring occasionally, and cook until just set.
Top warmed tortillas with scrambled eggs, sautéed swiss chard, pickled swiss chard stems, crumbled queso fresco, and sriracha (optional).