McDonald's (NYSE: MCD) and Restaurant Brands International (NYSE: QSR) have delivered strong earnings growth over the last few years, which has led both stocks to outperform the broader market averages. Recent sell-offs, however, are giving investors a good opportunity to add shares of these restaurant stocks to their portfolios. And that could make sense as both are on the offensive and capturing more spending from consumers who want better value and quicker service.In 2017, the Golden Arches stood tall over what was a very difficult consumer spending environment for restaurants as a whole.