Plugging $z=x^2+y^2$ into $2x-4y+z-6=0$ we get \begin{align*} 2x-4y+x^2+y^2-6&=0\\\ x^2+2x+\color{red}{1}+y^2-4y+\color{red}{4}&=6+\color{red}{1+4}\\\ (x+1)^2+(y-2)^2&=11 \end{align*}
Then, a parameterization for the curve is $$\begin{cases}x&=\sqrt{11}\cos t-1 \\\ y&=\sqrt{11}\sin t+2\\\z&=2\sqrt{11}(2\sin t -\cos t)+16\end{cases}\qquad 0\le t\le 2\pi$$