Set a large skillet over medium heat and add olive oil.
Add potatoes, sprinkle with salt and pepper, and cook, stirring now and then, until tender and browned all over. This will take about 10-15 minutes.
Add the tomatoes and spinach, add a little more salt and pepper, and cook, stirring, until spinach is wilted, 1-2 minutes. Add green onion and toss to combine. Remove from heat and set aside.
Cook the eggs using any method you like. I think fried or poached works best here.
While the eggs are cooking, microwave the butter just until melted, and stir in the harissa and a pinch of salt (if using unsalted butter).
To serve, transfer the potato mixture to two bowls and drizzle with some of the harissa butter. Top with eggs, add the rest of the harissa butter and serve immediately.