Heat a large frying pan (preferably cast iron) on medium, then add the olive oil and melt the butter.
Add the onions and saute until they're starting to soften, about 4 minutes.
Add the potatoes and minced garlic and stir, until coated with the butter. Season with some initial salt and pepper (you'll add more later), and cook until they start to gain golden brown color.
Then cover and cook to steam the potatoes until they are almost fork-tender, about 7 minutes (depending on the size of your potato pieces).
Uncover the pan and add a little more salt and pepper along with a tiny bit of dill. Cook, stirring frequently, until the potatoes are lightly browned.
Add the salmon and cook only until the salmon is heated through. Stir the mixture gently, being careful not to break up the salmon pieces too much. Taste and adjust the seasoning as desired. Right before turning off the heat, add the minced fresh herbs.
Serve immediately, alone or with feta crumbles, capers, eggs...whatever strikes your fancy!