d <- data.frame(x = rnorm(100, 0, 1),
            y = rnorm(100, 0, 1),
            z = rnorm(100, 0, 1))

func <-function(d){
  fit1 <- lm( y~ x + z, data = d)
  fit2 <- lm( y~x + I(z^2), data = d)
  fit3 <- lm( y~poly(x,3) + z, data = d)
  fit4 <- lm( y~ns(x, 3) + z, data = d)
  l <- list(fit1, fit2, fit3, fit4, fit5)
  names(l) <- paste0("fit", 1:5)
  return(l)
}

mods <- func(d)
mods[[1]]

stargazer(mods, type="text)