Melt oil in a large stockpot over medium-high heat. Add onions and salt, stir to coat and cook for 5-10 minutes, stirring occasionally, until the onions have softened. Add the garlic, and cook for 2 minutes until fragrant. Add ginger, cayenne, celery, kale, broccoli, and stir well to coat. Add water or broth, bring to a simmer and let cook for 4-5 minutes until the broccoli has softened. Remove from heat and let cool slightly.