Cook the bacon in a 10-inch cast-iron skillet over medium-high heat, stirring occasionally, until browned and crisp, 4 to 7 minutes. Remove to a paper towel-lined plate with a slotted spoon, reserving the drippings in the skillet. Add the potatoes to the skillet and season with 3/4 teaspoon salt and a few grinds of pepper. Cook, stirring occasionally, until browned and tender, 8 to 12 minutes. Add the onion, season with salt and continue cooking until the onion is lightly browned and the potatoes are cooked through, 3 to 5 minutes.
Add the squash and bacon to the skillet; reduce the heat to low (or move the skillet to a cooler part of the campfire). Use the back of a spoon to make 4 shallow wells in the potato mixture; carefully crack 1 egg into each well. Scatter the tomatoes around the eggs, cover the skillet and cook until the egg whites are set but the yolks are still runny, 6 to 12 minutes.
Season the eggs with salt and pepper; sprinkle with parsley before serving.
You can make these dishes over a campfire or on the stove. Use the lower end of the time range if cooking over a campfire.