First, cut the cabbage down the middle, splitting it into two equal halves. Locate the hard, white core for each half. Carefully cut out and discard the core. Next, place each half flat side down and cut into 2-inch strips then turn the cabbage 90 degrees and slice the strips into squares with a series of vertical cuts perpendicular to the ones you just made. Note: it doesn't have to be perfect. We're going for bite-sized pieces that will cook evenly.
Place a large heavy-bottomed skillet over medium heat. Add the neutral oil–as soon as it starts to shimmer add in the sliced garlic, ginger and scallion whites. Sauté, stirring frequently until the garlic starts to turn golden brown, about 5-7 minutes.
Next, increase the heat to medium-high and add in the cabbage and a generous pinch of salt. Depending on the size of your skillet (and your cabbage) you may need to do this in batches, adding more cabbage in as the first batch cooks down. Sauté the cabbage until its soft and tender but still has a bit of bite left, about 8-10 minutes, stirring often.
Last, add in the spinach, chili oil, soy sauce and sesame seeds. Toss to coat. Taste and adjust the seasoning as needed. Transfer the cabbage to a bowl and top with the reserved sliced scallion greens. Serve warm.